20Overview of the Unified C++ Interfaces

What is the Unified C++ API?

Unified C++ APIs for XML tools represent a set of C++ interfaces for Oracle XML tools. This unified approach provides a generic, interface-based framework that allows XML tools to be improved, updated, replaced, or added without affecting any interface-based user code, and minimally affecting application drivers and, possibly, application configuration. All three kinds of C++ interfaces: abstract classes, templates, and implicit interfaces represented by generic template parameters, are used by the unified framework.

Note:

Use the new unified C++ API in xml.hpp for new XDK applications. The old C++ API in oraxml.hpp is deprecated and supported only for backward compatibility, but will not be enhanced. It will be removed in a future release.

These C++ APIs support the W3C specification as closely as possible; however, Oracle cannot guarantee that the specification is fully supported by our implementation because the W3C specification does not cover C++ implementations.

Accessing the C++ Interface

The C++ interface is provided with Oracle Database. Sample files are located in $ORACLE_HOME/xdk/demo/cpp.

readme.html in the root directory of the software archive contains release specific information including bug fixes and API additions.

OracleXML Namespace

OracleXml is the C++ namespace for all XML C++ interfaces. It contains common interfaces and namespaces for different XDK packages. The following namespaces are included:

Ctx - namespace for TCtx related declarations

Dom - namespace for DOM related declarations

Parser - namespace for parser and schema validator declarations

IO - namespace for input and output source declarations

Xsl - namespace for XSLT related declarations

XPath - namespace for XPath related declarations

Tools - namespace for Tools::Factory related declarations

OracleXml is fully defined in the file xml.hpp. Another namespace, XmlCtxNS, visible to users, is defined in xmlctx.hpp. That namespace contains C++ definitions of data structures corresponding to C level definitions of the xmlctx context and related data structures. While there is no need for users to know details of that namespace, xmlctx.hpp needs to be included in most application main modules.

Multiple encodings are currently supported on the base of the oratext type that is currently supposed to be used by all implementations. All strings are represented as oratext*.

OracleXML Interfaces

XMLException Interface - This is the root interface for all XML exceptions.

Ctx Namespace

The Ctx namespace contains data types and interfaces related to the TCtx interface.

OracleXML Datatypes

error_language - gets overwritten by the language of the error handler, if specified

DATATYPE encodings - array of encodings.

Ctx Interfaces

ErrorHandler Interface - This is the root error handler class. It deals with local processing of errors, mainly from the underlying C implementation. It may throw XmlException in some implementations. But this is not specified in its signature in order to accommodate needs of all implementations. However, it can create exception objects. The error handler is passed to the TCtx constructor when TCtx is initialized. Implementations of this interface are provided by the user.

MemAllocator Interface - This is a simple root interface to make the TCtx interface reasonably generic so that different allocator approaches can be used in the future. It is passed to the TCtx constructor when TCtx is initialized. It is a low level allocator that does not know the type of an object being allocated. The allocators with this interface can also be used directly. In this case the user is responsible for the explicit deallocation of objects (with dealloc).

If the MemAllocator interface is passed as a parameter to the TCtx constructor, then, in many cases, it makes sense to overwrite the operator new. In this case all memory allocations in both C and C++ can be done by the same allocator.

Tctx Interface - This is an implicit interface to XML context implementations. It is primarily used for memory allocation, error (not exception) handling, and different encodings handling. The context interface is an implicit interface that is supposed to be used as type parameter. The name TCtx will be used as a corresponding type parameter name. Its actual substitutions are instantiations of implementations parameterized (templatized) by real context implementations. In the case of errors XmlException might be thrown.All constructors create and initialize context implementations. In a multithreaded environment a separate context implementation has to be initialized for each thread.

IO Namespace

The IO namespace specifies interfaces for the different input and output options for all XML tools.

Tools Interfaces

Factory - XML tools factory. Hides implementations of all XML tools and provides methods to create objects representing these tools based on their ID values.

Error Message Files

Error message files are provided in the mesg subdirectory. The messages files also exist in the $ORACLE_HOME/xdk/mesg directory. You can set the environment variable ORA_XML_MESG to point to the absolute path of the mesg subdirectory, although this not required.